1. Field of the Invention
The present invention relates generally to nuclear reactor steam generators, and more particularly to a closure for a steam generator wrapper penetration or access opening, and a method of installing the same within the wrapper from a position external to the steam generator pressure vessel or outer shell, such that once the wrapper penetration or access opening has been utilized for its intended purposes, the penetration or opening may be closed and the fluidic integrity of the generator wrapper restored.
2. Description of the Prior Art
A nuclear reactor produces heat as a result of the fission of nuclear material which is disposed within fuel rods, and the fuel rods are secured together in predetermined arrays so as to define fuel assemblies. The fuel assemblies, in turn, define the nuclear reactor core, and the core is disposed within a reactor or pressure vessel. In commercial nuclear reactor facilities, the heat produced by means of the aforenoted fission processes is utilized to generate electricity. In particular, a conventional facility may comprise, for example, a primary coolant flow and heat exchange or transfer loop to which conventional steam generators and steam turbines, as well as electrical generators, are fluidically and mechanically connected, respectively. A typical energy conversion process for such commercial nuclear reactor facilities would therefore comprise, for example, the transfer of heat from the nuclear reactor core to the primary coolant flow and loop system, and from the primary coolant flow and loop system to the steam generators by means of suitable heat exchangers incorporated within the steam generators. The steam generated within the steam generators is then of course transmitted to the steam turbines to which the electrical generators are operatively connected, and from which electricity is ultimately generated.
With reference initially being made to FIG. 1 of the drawings, a conventional steam generator structure or facility is disclosed. In particular, the steam generator is seen to comprise a vertically oriented, elongated entity which includes a hollow, substantially cylindrical pressure vessel or outer shell 12 having an upper shell section 14, a lower shell section 16, and a transition zone section 18 integrally interconnecting together the upper and lower shell sections 14 and 16. The diametrical extent of the upper shell section 14 is greater than that of the lower shell section 16, and consequently, the transition zone section 18 has the configuration of a conical frustum. A multitude of steam generator heat exchanger tubes 20 extend vertically within the central portion of the lower shell section 16 of the steam generator so as to define together a tube bundle. The uppermost portion of each of the tubes 20 extends upwardly within the transition cone section 18 of the steam generator and is seen to have an inverted U-shaped configuration. In this manner, the lower extremities of each tube 20 can be fixedly secured within a tube sheet 22 disposed within the lower end of the lower shell section 16. Integrally formed or secured to the outer periphery of the lower end of the lower shell section 16 within virtually the same horizontal plane as that of the tube sheet 22 is an annular support ring 24 by means of which the entire steam generator structure is capable of being supported upon the nuclear reactor facility or plant foundation. The lowermost end of the steam generator lower shell section 16 is sealingly enclosed by means of a hemispherically shaped shell portion 26, and disposed within hemispherical shell 26 is a vertically oriented divider plate 28 which serves to divide hemispherical shell 26 into two spherical quadrants. As may readily be appreciated, each of the quadrants is fluidically connected to one of the extremities of each of the heat exchanger tubes 20, and the quadrants are also provided with a fluid nozzle 30 and 32, respectively, which serve to introduce nuclear reactor core coolant into, and discharge nuclear reactor core coolant from, the steam generator. In this manner, during operation of the nuclear facility, primary core coolant is conducted throughout its heat exchange or transfer loop from the nuclear reactor core, not shown, through inlet nozzle 30, the left steam generator hemispherical shell quadrant 34, the steam generator tube bundle U-shaped heat exchanger tubes 20, the right steam generator hemispherical shell quadrant 36, as viewed in FIG. 1, outlet nozzle 32, and back to the nuclear reactor core.
In order to provide for the generation of steam within the steam generator, an inlet feedwater nozzle 38 is provided within a sidewall portion of the upper shell section 14 of the steam generator, and a water conduit 40 is disposed internally of nozzle 38. The conduit 40 is integrally connected with an annular manifold 42 which has operatively associated, in a fluidically connected manner, a multitude of upstanding, inverted J-tubes or nozzles 44 through means of which the incoming feedwater is projected downwardly in cascading sheets. In order to define a flowpath for the cascading water flowing downwardly through the steam generator, the entire tube bundle is enveloped or encased within a cylindrical tube wrapper 46 which extends vertically, and substantially concentrically, within the lower and transitional zone sections 16 and 18 of the steam generator shell 12, the tube wrapper 46 being fixedly secured within the shell 12 by suitable means, not shown. In this manner, the tube wrapper 46 and the lower and transitional zone sections 16 and 18 of the shell 12 serve to define an annular downcomer region 48 through which the water flows downwardly toward the bottom of the steam generator facility. It is seen that the lower peripheral edge of the tube wrapper 46 is suspended above the upper surface of the tube sheet 22 whereby a transverse flow region is defined between the downcomer region 48 of the generator and the tube bundle section of the generator which is disposed internally of the tube wrapper 46. The water therefore enters the tube bundle section of the generator, and the heat exchange process between the water and the heat tube bundle tubes 20, through which the hot reactor core coolant is being conducted and circulated, begins to take place with the water passing between all of the heat exchange tubes 20. As a result, steam is generated, and the water and steam flow upwardly through the entire tube bundle, between the tubes 20, under natural convection. In order to provide lateral support and stabilization for the heat exchange tubes 20 throughout their vertical extent, a plurality of horizontally disposed, vertically spaced tube support plates 50 are fixedly secured to the interior wall surface of the tube wrapper 46. As is conventional, the heat exchanger tubes 20 pass through holes or apertures 52 defined within the tube support plates 50, there being sufficient spatial clearance defined between the tubes 20 and the plate apertures or holes 52 so as to provide for the desired, limited lateral support and restricted movement of the tubes 20, in response to the water flow thereabout as well as thermal expansion and contraction conditions, without hindering the passage therethrough of the water and steam flowing upwardly through the generator. It is to be further noted that in view of the U-shaped configuration of the tubes 20, a tube-passageway or lane 54 is defined between the legs of the tubes 20, and within each of the horizontally disposed support plates 50, with the exception of the lowermost plate 50', there are defined a plurality of radially aligned slots 56 through which water and steam may likewise pass from one vertically spaced or defined section of the generator heat exchanger portion to another. The lowermost support plate 50' has the configuration of an annular disc with the central portion thereof open, and in this manner, the plate 50' serves as a flow distribution baffle which effectively causes a high percentage of the incoming water to flow from the radially outer portion of the tube bundle section of the steam generator, beneath the undersurface of the plate or baffle 50', and upwardly through the large central aperture defined within the plate or baffle 50', with the remaining portion of incoming water flow passing upwardly through the apertures or holes 52 defined within plate or baffle 50' Water and steam can therefore flow upwardly through the various vertically spaced stages of the heat exchanger, through means of the holes or apertures 52, as well as the slots 56 and the lanes 54, in a predeterminedly defined pattern which seeks to achieve flow uniformity. In addition to the support plates 50, antivibration bars 58 may be provided within the uppermost portion of the wrapper 46 so as to engage the uppermost, U-shaped bent sections of the heat exchanger tubes 20 for likewise performing restrictive and stabilizing functions with respect to tubes 20 in a manner similar to that of support plates 50 under steam and water flow, as well as thermal expansion and contraction, conditions. As a result, excessive wear of the heat exchanger tubes 20 is effectively prevented or substantially reduced, as is vibrational noise.
The upper end of the steam generator heat exchanger tube wrapper 46 is integrally provided with a horizontally disposed deck or cover 60 so as to seal the interior of the wrapper 46 within which the heat exchanger U-bent tubes 20 are disposed, however, in order to permit the upward escape of the generated steam from the heat exchanger portion of the generator and out of the wrapper 46, a plurality of holes or bores 62 are defined within the cover or deck 60. A plurality of upstanding swirl vane primary moisture separators 64, in the form of, for example, cylindrical tubes approximately twenty inches (20") in diameter, are vertically supported atop tube wrapper deck or cover 60 with the lower ends thereof respectively in fluidic communication with the apertures or holes 62. A pair of horizontally disposed, vertically spaced lateral support plates 66 are fixedly secured with respect to the moisture separator tube systems at the upper ends and the axially central portions thereof, and in particular, it is seen that a plurality of apertures 68 are defined within the axially central or lower support plate 66 so as to permit the separator tubes 64 to pass therethrough. A plurality of outer cylindrical casings 70 concentrically surround those portions of the swirl vane separator tubes 64 which are interposed between the lateral support plates 66, and the upper ends of the casings 70 are in contact with the undersurface of the lower lateral support plate 66. Orifice bushings 72, having a diametrical extent which is less than that of the casings 70, are disposed within apertures 74 defined within the upper lateral support plate 66 such that the upper ends of the bushings 72 extend slightly above the upper surface of the upper support plate 66 while the lower ends of the bushings 72 are disposed within the upper ends of the casings 70. The upper ends of the swirl vane separator tubes 64 terminate at a level within the casings 70 which is below that of upper lateral support plate 66, and in this manner, water thrown radially outwardly under centrifugal force as a result of the passage of the water/steam mixture through the swirl vane separator tubes 64, and in particular past the swirl vane separators 76 respectively disposed within each tube 64, can collect upon the inner surface of each casing 70 while the steam can continue to travel axially upwardly so as to pass through the upper ends of the separator casings 70 and orifice bushings 72. The lower ends of the casings 70 are provided with rectangularly shaped cut-outs or apertures 78 so as to permit the aforenoted separated water to pass outwardly therethrough and over the peripheral edge of the lower lateral support plate 66 and be discharged back into the downcomer region 48 for recirculation back upwardly through the heat exchanger tube bundle within wrapper 46.
Within the uppermost section of the steam generator shell portion 14, there is defined a steam dome chamber 80 into which the steam exiting from the orifice bushings 72 enters, and within which there is disposed a plurality of stacked positive entrainment steam dryers 82. The dryers 82 have the configurations of cubes or rectangular parallelepipeds, and the upper surface of the upper dryer 82 is open so as to mate with a similarly configured cut-out or aperture 84 defined within a divider plate 86 disposed within the steam dome chamber 80. In this manner, the steam exiting from the orifice bushings 72 and passing into the steam dome chamber 80 is forced to enter the sidewalls of the dryers 82 before being further passed through dryers 82 and upwardly out of dryer opening 84 for discharge from the steam generator through means of an axially upstanding steam nozzle 88 disposed atop the steam generator. The dryers 82 serve to separate any remaining or residual water vapor entrained within the steam before the latter is conducted to the steam nozzle 88 for further passage to the steam turbines and electrical generators, not shown, and any such separated water is conducted vertically downwardly to a suitable pool or reservoir 89, defined within the central portion of the wrapper deck or cover 60, by means of an axially central drain pipe 90 dependently fixed to the floor 92 of the lower dryer 82. The lower terminal end of pipe 90 is vertically spaced above wrapper deck or cover 60, and in this manner, the water collected within reservoir or pool 89 may ultimately flow radially outwardly over the wrapper deck or cover 60 so as to cascade downwardly into the annular downcomer region 48 in a manner similar to the separated water exiting from the cut-outs or apertures 78 defined within the separator casings 70.
Having now generally described the structural composition of a conventional steam generator, it is well known that various holes, apertures, or bores are provided within various different sidewall portions, for example, of the steam generator wrapper for various different purposes, such as, for example, to house various different types of instrumentation necessary to the operation or monitoring of the operation of the generator, to provide visual inspection means within the generator, to provide manipulative access means within the generator wrapper so as to facilitate, for example, the removal or replacement of various parts of the generator, and the like. Upon completion of the various operational inspection apparatus, measuring or monitoring instrumentation or equipment, or the maintenance or repair apparatus, the wrapper through-bores must be closed and sealed so as to restore the fluidic integrity or boundary defined within the steam generator by means of the generator wrapper. Heretofore, while such penetrations also encompassed appropriate bores or access openings likewise defined within the steam generator outer shell or pressure vessel, closure of the shell or vessel could be readily accomplished in view of the fact that both maintenance personnel and the necessary tool systems and equipment would be disposed externally of the shell or vessel. In order to similarly accomplish the closure and sealing of the generator wrapper, however, such procedures must of necessity be able to be accomplished within the restricted confines defined interiorly of the pressure vessel or outer shell which has heretofore proven to be difficult to achieve. In addition, prior art wrapper closure designs or systems were operatively affixed upon the pressure vessel or outer shell, and consequently, such designs or systems severely limited the relative movement of the generator wrapper with respect to the generator outer shell or pressure vessel under both fluid flow pressure differential, as well as thermal contraction and expansion differential, conditions. If a predetermined amount of relative movement of the generator wrapper relative to the generator vessel or shell is not permitted, then deleterious stresses would be induced within the wrapper under such pressure and thermal differential conditions, whereby, ultimately, rupture, corrosive fatigue, and the like, would probably manifest itself within the generator wrapper.
Accordingly, it is an object of the present invention to provide a new and improved steam generator tube bundle wrapper closure plug assembly and a method of installing the same.
Another object of the present invention is to provide a new and improved steam generator tube bundle wrapper closure plug assembly, and a method of installing the same, which overcomes various noted characteristics associated with conventional generator wrapper closure assemblies.
Still another object of the present invention is to provide a new and improved steam generator tube bundle wrapper closure plug assembly, and a method of installing the same, which may be simply and readily installed within the steam generator tube bundle wrapper from a position external to the steam generator outer shell or pressure vessel.
Yet another object of the present invention is to provide a new and improved steam generator tube bundle wrapper closure plug assembly, and method of installing the same, which does not adversely affect the limited movement of the wrapper relative to the steam generator outer shell or pressure vessel under differential pressure or thermal conditions.
Still yet another object of the present invention is to provide a new and improved steam generator tube bundle wrapper closure plug assembly, and a method of installing the same, wherein the assembly is, in effect, a self-contained unit which facilitates insertion, installation, and fixation of the closure assembly within and upon the steam generator wrapper so as to restore the integrity of the fluidic boundary defined by means of the steam generator wrapper.
Yet still another object of the present invention is to provide a new and improved steam generator tube bundle wrapper closure plug assembly, and a method of installing the same, wherein the assembly is particularly well-suited for the sealing and closing of "hillside-type" penetrations defined within a steam generator tube bundle wrapper, "hillside-type" penetrations being those penetrations which extend in a radially oriented direction through both the steam generator outer shell or pressure vessel, and the tube bundle wrapper, however, the penetrations are not in fact radially aligned so as to facilitate, for example, the insertion or introduction of suitable instrumentation or inspection equipment without interfering with, encountering, or damaging the U-shaped heat exchanger tubes housed internally within the steam generator wrapper.